- "This isn't you, Andy. The man I knew pulled me out of dark waters. Convinced me to keep going when I didn't see the point."
- —John Diggle trying to get through to his brother
"Dark Waters" is the ninth and midseason finale episode of the fourth season of , and the seventy-eighth episode overall. It aired on December 9, 2015.
|After the city is attacked again, Oliver makes a bold move against HIVE. Malcolm checks in on Thea and leaves her with a warning. Things take a horrible turn when Damien Darhk retaliates in a brutal manner at Oliver's mayoral holiday party.|
Oliver encourages citizens to clean up the Star City Bay, prompting Darhk to send a drone attack. Felicity takes it down, but many are injured. In retaliation, Oliver reveals Darhk's photo, declaring him the leader of the Ghosts, on television and sets up a hotline for anyone who has any information about him. Darhk, watching on television with other H.I.V.E. members, is visibly enraged and breaks the television with his magic. Milo Armitage makes a sarcastic remark about his fame.
Reluctantly, Oliver and the others go through with a holiday party to show they are not afraid. Andy Diggle continues to be uncooperative with his brother Meanwhile, Felicity's mother Donna discover's Oliver's engagement ring and shows it to her daughter. At the holiday party, Felicity learns that her mother is dating Quentin Lance. Later, she and Oliver meet Curtis's husband, Paul. During their discussion, Felicity realizes Oliver was going to propose the night Laurel and Thea came to Ivy Town to ask for their help. Felicity wonders why Oliver didn't try to propose again. He says that everything changed and he wasn't sure if he could anymore.
Darhk crashes the party despite high security. He knocks out Oliver and kidnaps Diggle, Thea and Felicity. Oliver and Laurel go out to beat on the Ghosts to get a location, but come up with nothing. Malcolm arrives in the Arrowcave, surprising Quentin, and provides a communicator that the Ghosts use. Oliver offers himself up to Darhk, who takes him back to HIVE HQ. Laurel and Malcolm, who is dressed as the Green Arrow, follow, using a nanotracker in Oliver's bloodstream.
Darhk demonstrates algae that HIVE is growing in the bay, which they are trying to adapt to make breathable. They test it on humans, who they put in a gas chamber. He lets Oliver have one last conversation with Felicity who says she would have agreed to marry him. Darhk decides that, although Oliver is agreeing to work with him now, it is easier to remove all motivation for resistance and kill Thea, Diggle, and Felicity in the gas chamber. Laurel and Malcolm arrive, with Laurel's Canary Cry breaking the glass and freeing the captives. The other members of HIVE escape, while Malcolm and Oliver go after Darhk. After a fight, Malcolm leaves Damien pinned to the ground with arrows and right next to an exploding arrow. Quentin and a squad of cops help the others escape from the many HIVE pledges.
Later, Oliver holds another tree lighting where he proposes. As the new fiancés return home, their limo is attacked by Ghosts. The driver is killed and Oliver leaves Felicity in the back as he drives them to safety. Meanwhile, Damien enjoys decorating his Christmas tree with his wife and young daughter. Oliver opens the door of the limo and finds an unresponsive Felicity with a slight of blood coming out of her mouth.
In the flashback, Oliver heads underwater to the ship and upon his return, was ambushed by Conklin.
- Stephen Amell as Oliver Queen
- Katie Cassidy as Laurel Lance/Black Canary
- David Ramsey as John Diggle
- Willa Holland as Thea Queen
- Emily Bett Rickards as Felicity Smoak
- John Barrowman as Malcolm Merlyn/Green Arrow
- Paul Blackthorne as Captain Quentin Lance
Special appearance by
- Eugene Byrd as Andy Diggle
- Charlotte Ross as Donna Smoak
- Echo Kellum as Curtis Holt
- Ryan Robbins as Conklin
- Elysia Rotaru as Taiana Venediktov
- Parker Young as Alex Davis
- Lynda Boyd as Phaedra Nixon
- Janet Kidder as Ruvé Adams
- James Kidnie as Milo Armitage
- Keri Adams as Bethany Snow
- Alison Araya as Officer Lopez
- Joel Cottingham as Prisoner #2
- Jason Duiven as Ghost
- Sam Dulmage as Prisoner #1
- Ava Frye as Young Girl with Glasses
- Marrett Green as Reporter
- Tuesday Hofmann as Darhk's Daughter
- Chenier Hundal as Paul
Preparation ran from October 5 until October 14, 2015. Shooting ran from October 15 until October 27, 2015.
- Oliver finally proposes to Felicity, though his marriage to Nyssa al Ghul under League of Assassins law wasn't brought up to address this.
- This conflict was resolved by Nyssa in the Season 6 episode "".
- Donna Smoak says "humbug", referencing the phrase used by the protagonist of Charles Dickens' A Christmas Carol, Ebenezer Scrooge.
- This is the first episode of Arrow that Oliver doesn't fire an arrow in.
- This episode marks the first time that Malcolm Merlyn dons the Green Arrow suit.
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